Index: contrib/netbsd-tests/lib/libc/regex/data/meta.in
===================================================================
--- contrib/netbsd-tests/lib/libc/regex/data/meta.in
+++ contrib/netbsd-tests/lib/libc/regex/data/meta.in
@@ -4,7 +4,9 @@
 a\*c		&	a*c	a*c
 a\\b		&	a\b	a\b
 a\\\*b		&	a\*b	a\*b
-a\bc		&	abc	abc
+# Begin FreeBSD
+a\bc		&C	EESCAPE
+# End FreeBSD
 a\		&C	EESCAPE
 a\\bc		&	a\bc	a\bc
 \{		bC	BADRPT
Index: lib/libc/regex/regcomp.c
===================================================================
--- lib/libc/regex/regcomp.c
+++ lib/libc/regex/regcomp.c
@@ -97,6 +97,7 @@
 static void p_b_eclass(struct parse *p, cset *cs);
 static wint_t p_b_symbol(struct parse *p);
 static wint_t p_b_coll_elem(struct parse *p, wint_t endc);
+static int may_escape(struct parse *p, const wint_t ch);
 static wint_t othercase(wint_t ch);
 static void bothcases(struct parse *p, wint_t ch);
 static void ordinary(struct parse *p, wint_t ch);
@@ -436,7 +437,10 @@
 			EMIT(OEOW, 0);
 			break;
 		default:
-			ordinary(p, wc);
+			if (may_escape(p, wc) == 0)
+				ordinary(p, wc);
+			else
+				SETERROR(REG_EESCAPE);
 			break;
 		}
 		break;
@@ -653,7 +657,11 @@
 	default:
 		p->next--;
 		wc = WGETNEXT();
-		ordinary(p, wc);
+		/*  Throw an error if we're not dealing with an escapable */
+		if (c&BACKSL && may_escape(p, wc) != 0)
+			SETERROR(REG_EESCAPE);
+		else
+			ordinary(p, wc);
 		break;
 	}
 
@@ -930,6 +938,46 @@
 }
 
 /*
+ - may_escape - determine whether 'ch' is escape-able in the current context
+ == static int may_escape(struct parse *p, const wint_t ch)
+ */
+static int
+may_escape(struct parse *p, const wint_t ch)
+{
+	/*
+	 * Build a whitelist of characters that may be escaped to produce an
+	 * ordinary in the current context. This assumes that these have not
+	 * been otherwise interpreted as a special character. Escaping an
+	 * ordinary character yields undefined results according to
+	 * IEEE 1003.1-2008. Some extensions (notably, some GNU extensions) take
+	 * advantage of this and use escaped ordinary characters to provide
+	 * special meaning, e.g. \b, \B, \w, \W, \s, \S.
+	 */
+	switch(ch) {
+	case '(':
+	case ')':
+	case '+':
+	case '{':
+	case '}':
+	case '?':
+		/* The above characters may not be escaped in BREs */
+		if (!(p->g->cflags&REG_EXTENDED))
+			return 1;
+		/* Fallthrough */
+	case '.':
+	case '[':
+	case ']':
+	case '\\':
+	case '*':
+	case '^':
+	case '$':
+		return 0;
+	default:
+		return 1;
+	}
+}
+
+/*
  - othercase - return the case counterpart of an alphabetic
  == static wint_t othercase(wint_t ch);
  */
Index: lib/libc/regex/regerror.c
===================================================================
--- lib/libc/regex/regerror.c
+++ lib/libc/regex/regerror.c
@@ -90,7 +90,7 @@
 	{REG_BADPAT,	"REG_BADPAT",	"invalid regular expression"},
 	{REG_ECOLLATE,	"REG_ECOLLATE",	"invalid collating element"},
 	{REG_ECTYPE,	"REG_ECTYPE",	"invalid character class"},
-	{REG_EESCAPE,	"REG_EESCAPE",	"trailing backslash (\\)"},
+	{REG_EESCAPE,	"REG_EESCAPE",	"invalid escape sequence or trailing backslash (\\)"},
 	{REG_ESUBREG,	"REG_ESUBREG",	"invalid backreference number"},
 	{REG_EBRACK,	"REG_EBRACK",	"brackets ([ ]) not balanced"},
 	{REG_EPAREN,	"REG_EPAREN",	"parentheses not balanced"},